The present invention relates generally to exhaust-gas turbochargers for internal combustion engines, and more particularly to an inexpensive apparatus and associated method to prevent undesired backup of lubricating oil into the turbine wheel housing formed on the hot side of a turbocharger.
As is well known, exhaust-gas turbochargers are utilized on a large number of internal combustion engines to increase peak horsepower and performance. Nearly all of such conventional turbochargers utilize a lubrication system wherein oil is supplied under pressure to the turbine bearing housing through an inlet port into the interior of the turbocharger and subsequently ported through internal flow channels to lubricate the bearings of the turbocharger shaft. Subsequently, a common outlet or drain is provided at the lower most portion of the turbocharger housing, wherein the oil drains by gravity to an oil sump. In view of the high temperatures and pressures encountered in operation of the turbocharger, the oil lubricant typically is discharged adjacent the outlet port in an aerated or foamed condition and as such, there is a tendency for such foamed oil to backup adjacent the outlet port and occasionally seep or back flow into the interior of the turbine wheel housing formed on the hot side of the turbocharger. When such a back flow condition occurs, the turbine undesirably burns oil and/or throws oil during operation.
In recognition of the inherent deficiencies of such prior art lubrication systems, it has heretofore been customary to mount all turbochargers at the highest possible vertical elevation or location relative to the engine, sometimes requiring modification of the engine compartment cover or hood, such that oil discharged through the outlet port has a sufficiently long drain conduit to avoid excessive backup. With the ever shrinking room availability for engines within modern motor vehicle, boating and aviation applications, however, it is oftentimes difficult, if not impossible to mount turbochargers at a high enough elevation relative to the engine to completely avoid such oil backup.
It is additionally known in the prior art for racing applications, to utilize a dry-sump pump system which basically comprises an auxiliary pump being utilized to apply a vacuum to the oil outlet port of the turbocharger and pull the drain oil therefrom. However, such modern racing application systems are typically driven mechanically from power obtained from the cam shaft of the engine or through an auxiliary electric motor, both of which are subject to failure during prolonged use and are costly to install and maintain.
A variety of other prior art approaches have been applied to turbocharger lubrication. For example, in U.S. Letters Pat. No. 4,009,972 issued to Sarle, the turbocharger is modified such that an air pressure bleed from the turbocharger compressor is diverted to the turbocharger oil sump exhaust line to assist oil flow from the turbocharger by virtue of a pressure differential. Another approach disclosed in U.S. Pat. No. 3,740,170 issued to Miller, utilizes a separate gear pump to supply oil to the turbocharger inlet, while relying on gravity to return the oil from the turbocharger. In yet another approach, disclosed in U.S. Letters Pat. No. 4,752,193 issued to Horler, a separate gear or vane pump is utilized to supply lubricant to the inlet of the turbocharger while a low pressure boost air pipe is utilized to aid oil return. U.S. Letters Pat. No. 4,525,995 issued to Clark depicts a lubrication system specifically adapted to gas turbine engines wherein oil is scavenged from the turbocharger cavity by allowing high pressure air from the compressor section of the engine to leak into the cavity and then flow downwardly together with the entrained scavenged oil from the turbocharger. Yet another approach, disclosed in U.S. Letters Pat. No. 4,511,016 issued to Doell, also adapted to gas turbine engines, utilizes a primary and auxiliary lubricant circulating circuit to provide a lubricant supply to the engine lubricating chamber.
These prior art lubrication systems, however, either require the use of auxiliary equipment driven by the engine cam shaft or an auxiliary electric motor, and/or require modifications to the turbocharger itself, and/or simply rely on gravity for oil return, in which case the tendency for the turbocharger oil to backup continues to exist. Furthermore, as noted above, the auxiliary cam shaft or electric motor driven equipment used by some of these systems is costly to install as well as subject to failure during prolonged use. As such there exists a substantial need in the art for an improved turbocharger lubrication system which is low cost, reliable and eliminates the oil backup problems associated in the art.